1. Field of the Invention
The invention relates to a filter for the filtration of media, having a pleated, cylindrical filter element, which is located between a perforated, cylindrical backflow preventer and a perforated, cylindrical core, the filter element being arranged in pleated folds, a plurality of folds having a first fold height which is greater than the difference between the radius of the backflow preventer and the radius of the core and which, each being inclined in relation to a radial line by an angle of inclination, are directed away from the outer surface of the core.
2. Description of the Related Art
Optimized pleat and/or fold geometries are used in order to circumvent the classic problem of the star-shaped pleat fold arrangement in cylindrically shaped filter elements. This fold arrangement deploys radial folds of identical fold height, which are tightly pressed together on the smallest circumference on the core, but are located far apart on the outer circumference on the backflow preventer. In this manner, a large proportion of the space provided cannot be filled with filter material, and the mechanical stability of the filter element in the outer region is compromised by the potential for movement of the folds in the free spaces which are located in between. Filter surfaces which are achieved with two layers of membranes measure approximately 0.5 to 0.7 sq.m. per 10 inches of element.
An increase of the filter surface is often achieved by means of thinner filter materials, or in particular by thinner drainage and/or spacer materials. The number of folds per filter element and, therefore, the filter surface are thus increased. A disadvantageous consequence is a reduced mechanical stability of the folds made from these thinner materials. In addition, the inflow to the filter materials which are located between the folds is associated with an increasing flow resistance, when using thinner drainage and/or spacer materials. As a result, the throughput performance may drop despite a larger filter surface. Beyond this, there is the danger that the inflow can no longer pass to the end regions of the intermediate spaces between the folds, or that air pockets are formed. The filter surface in these regions then becomes inactive.
The fundamental endeavor is thus to increase the filtration performance as a function of throughput and service life.
DE 693 29 118 T2, DE 693 34 045 T2 and DE 693 33 430 T2, which belong to the same patent family, disclose a filter having a pleated, cylindrical filter element which is located between a backflow preventer and a core. The filter element here is formed with multiple layers and arranged in pleated folds which have a fold height which is greater than the difference between the radius of the outer cylinder and the radius of the core. The folds here are directed away in curved shaped from the outer surface of the core in a tangential direction and have an angle of inclination in relation to a radial line.
The fold height may be significantly increased here, these oversized folds being increasingly inclined tangentially towards the outer cylinder, such that a space which has hitherto not been filled with filter material may also be filled up to the outer cylinder.
However, the long intermediate spaces which have to be perfused between folds in this known filter are disadvantageous. There is the danger that the inflow can no longer pass to the end regions of the intermediate spaces between the folds, or that air pockets are formed. The filter surface in these regions then becomes inactive.
Furthermore, DE 39 35 503 C2 discloses a ring filter element made from a filter material which has been folded in a zigzag shape with folds which are radially oriented and of different lengths in the direction of the radial depth, the shorter ones being located outside in the radial direction. Here, at least two long folds should follow each short one, the short and the long folds each having the same radial depth as viewed across the entire circumference.
In the case of these radially arranged long folds and the short folds located in between, it is disadvantageous that the available filter surface is relatively small, which leads to an insufficient filtration performance. Moreover, the stability of such filters needs improvement.
The object of the present invention is to improve the known filters in such a manner that their performance, and in particular their service life, are increased while good mechanical stability of the filter element is maintained simultaneously.